Scroll Fluid Machine

ABSTRACT

A scroll fluid machine is configured by engaging a fixed scroll and an orbiting scroll having spiral bodies formed on base plates. A seal member is provided between a rear surface of the orbiting scroll and a frame member arranged opposite thereto to divide a rear side chamber into an inner space and an outer space. The inner space inside the seal member is subjected to a pressure substantially corresponding to a discharge pressure, and the outer space is subjected to a pressure lower than that of an inner back pressure chamber to press the orbiting scroll against the fixed scroll. The scroll members are formed such that the width of a groove and the thickness of a tooth of the spiral body formed inside the seal member are larger than those of the spiral body formed outside the seal member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a scroll fluid machine which is a kind of positive displacement fluid machine used for a compressor, a vacuum pump, an expander and the like, and is suitable for a scroll compressor in particular.

2. Description of Related Art

Conventional scroll fluid machines are described in JP-A-08-121366 and JP-A-2004-293531.

In the one disclosed in JP-A-08-121366, a seal ring is provided between a seal surface on a wrap opposite side (on a rear chamber side) of an orbiting scroll member and a frame facing the seal surface and is held in a ring-shaped groove in the frame, and this seal ring divides an inner space which is located in the central portion and is at a pressure substantially equal to a discharge pressure and in which an oil supply path is opened to introduce lubricating oil accumulated in a bottom portion in a hermetic container to an upper portion, from an outer space which is located in an outer peripheral portion and is maintained at an intermediate pressure between a suction pressure and the discharge pressure.

By this division, pressure acts on the orbiting scroll member, depending on the pressures of both inner space and outer space, to press the orbiting scroll member to a fixed scroll member to achieve sealing between both members.

Further, a required minimum amount of lubricating oil is leaked on a top end surface of the seal ring from the inner space to the outer space by means of pressure difference, and a major part of residual lubricating oil remaining in the inner space is returned to the bottom portion in the hermetic container without allowing the residual oil to be mixed with compressed gas in the hermetic container. By this configuration, high reliability of a bearing, excellent compression efficiency, and low oil loss level can be obtained.

BRIEF SUMMARY OF THE INVENTION

In the case of the scroll fluid machines described in the prior arts described in JP-A-08-121366 and JP-A-2004-293531, since the inner space on the rear chamber side of the orbiting scroll member is subjected to the discharge pressure, and the outer space is subjected to the intermediate pressure between the suction pressure and the discharge pressure, there is the possibility that pressing force on the central portion side of the orbiting scroll member to the fixed scroll member becomes excessive to cause seizing and scoring on sliding surfaces of both scrolls.

An object of the present invention is to provide a scroll fluid machine which can prevent occurrence of seizing and scoring on the sliding surfaces of both scrolls by appropriately adjusting pressing force by which one scroll member is pressed against the other scroll member.

In order to achieve the above object, the present invention provides a scroll fluid machine in which two scroll members having spiral bodies formed on base plates are engaged to perform relative gyrating movement to enlarge or reduce a hermetic space formed by both scroll members so as to make fluid expand or compress the fluid, wherein the scroll fluid machine is configured such that the rear surface of one of the scroll members is divided into an inner space and an outer space by providing a seal member between the rear surface and a stationary member, and the inner space inside the seal member is subjected to a pressure substantially corresponding to a discharge pressure and the outer space outside the seal member is subjected to a pressure lower than that in an inner back pressure chamber so as to be pressed against the other scroll member, and wherein the shapes of the spiral bodies of the scroll members are configured such that widths of grooves of the spiral bodies of the scroll members decrease, and thicknesses of teeth of the spiral bodies also decrease, from central portions toward outer sides of the spiral bodies over a part of or the whole of the spiral bodies.

Here, it is preferable that a part of or the whole of the spiral body of the scroll member is formed by an involute of a circle (a base circle) having a radius which varies depending on an involute angle.

In addition, it is preferable that the scroll member is formed such that the groove width and the tooth thickness of the spiral body formed inside the seal member are larger than those of the spiral body formed outside the seal member.

Further, it is preferable that the scroll member has a radius where a radius of the base circle for forming the spiral body formed inside the seal member has a radius larger than that of the base circle for forming the spiral body formed outside the seal member. Here, the spiral body of the scroll member is formed preferably by an involute of a circle represented by:

a=as+f(λ) (f′(λ)<0)

wherein a is a radius of the base circle, λ is an involute angle, and as is a radius of the base circle at a beginning portion of winding of the spiral body.

Another feature of the present invention is that, in a scroll fluid machine configured by engaging a fixed scroll and an orbiting scroll having spiral bodies formed on base plates, the scroll fluid machine is configured such that a seal member is provided between the rear surface of the orbiting scroll and a frame member arranged opposite thereto to define an inner space and an outer space, and the inner space inside the seal member is subjected to a pressure substantially corresponding to a discharge pressure and the outer space outside the seal member is subjected to a pressure lower than that of an inner back pressure chamber to press the orbiting scroll against the fixed scroll, and wherein the orbiting scroll and the fixed scroll are formed such that the width of a groove and the thickness of a tooth of the spiral body formed inside the seal member are larger those of the spiral body formed outside the seal member.

According to the present invention, since the shape of the spiral body of the scroll member is configured such that the width of the groove of the spiral body of the scroll member decreases and the thickness of the tooth of the spiral body also decreases from the central portion toward the outer side of the spiral body over a part of or the whole of the spiral body, it is possible to properly adjust pressing force by which one scroll member is pressed against the other scroll member, and to obtain a scroll fluid machine which can prevent occurrence of seizing and scoring on the sliding surfaces of the scroll members.

Other objects, features and advantages of the invention will become apparent from the following description of an embodiment of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a vertical sectional view showing an embodiment of a scroll fluid machine of the present invention;

FIG. 2 is a view illustrating pressures acting on an orbiting scroll; and

FIGS. 3A and 3B are a plan view and a vertical sectional view, respectively, of the orbiting scroll shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will be described below using the drawings. A part denoted by the same reference numeral in the figures indicates the same part or a corresponding part.

Embodiment 1

An embodiment of the present invention will be described using FIGS. 1, 2 and 3. FIG. 1 is a vertical sectional view of a scroll compressor, FIG. 2 is a view illustrating pressures acting on an orbiting scroll, and FIGS. 3A and 3B are a plan view and a vertical sectional view of the orbiting scroll shown in FIG. 1, respectively.

In a scroll compressor 1, a compression mechanism portion 2, and a drive portion 3 which drive the compression mechanism portion and a rotational shaft 300 are accommodated in a hermetic container 700. FIG. 1 shows a vertical type scroll compressor, in which the drive portion 3 is disposed below the compression mechanism portion 2 via the rotational shaft 300, an oil reservoir 730 is disposed below the drive portion 3, and the compression mechanism portion 2 and the drive portion 3 are connected via the rotational shaft 300.

The compression mechanism portion 2 is configured from base elements of a fixed scroll 100, an orbiting scroll 200 and a frame 400, the frame 400 is fixed to the hermetic container 700, and a roller bearing 401 supporting the rotational shaft is disposed. The fixed scroll 100 is configured from base components of a base plate 101, a scroll spiral body 102, a suction port 103 and a discharge port 104, and is fixed to the frame 400 by a bolt 405. The scroll spiral body 102 is vertically provided upright on a surface on one side of the base plate 101. The orbiting scroll 200 is configured from base components of a base plate 201, a scroll spiral body 202, an orbiting scroll bearing portion 203 in which a sliding bearing 210 is disposed, and a back pressure hole formed in the base plate 201 to provide communication between a compression chamber and a back pressure chamber on a base plate rear side. The scroll spiral body 202 is vertically provided upright on a fixed scroll side of the base plate 201. The orbiting scroll bearing portion 203 is formed in the central portion on a spiral body opposite side of the base plate 201 to protrude vertically. The orbiting scroll 200 is fabricated by working a cast made of materials such as cast iron and aluminum.

The fixed scroll 100 and the orbiting scroll 200 are engaged to form the compression chamber 130. In the compression chamber 130, the orbiting scroll 200 gyrates to reduce the volume thereof to perform compression operation. In this compression operation, in connection with the gyrating movement of the orbiting scroll 200, a working fluid is sucked into the compression chamber 130 from a suction pipe 711 and the suction port 103, and the sucked working fluid is discharged in the hermetic container 700 from a discharge port 104 of the fixed scroll 100 after the compression process, and further discharged out of the hermetic container 700 via a discharge pipe 701. In this way, the space in the hermetic container 700 is maintained at a discharge pressure. As a working fluid to be compressed in the compression mechanism portion, an earth-friendly high pressure refrigerant such as R410A is used generally.

The hermetic container 700 has an upper cap 710 and a lower cap 720, which are fitted to cover an outer side of a middle cylindrical portion of the hermetic container, and is configured by heating and welding the fitting end portions by using a welding torch obliquely from below and obliquely from above. A leg portion 721 is attached to a bottom surface of the hermetic container 700, and a magnet 722 is disposed inside the lower cap 720 to collect coarse particulates in the compressor. Further, a hermetic terminal 702 and a terminal cover 703 are provided on a side surface of the hermetic container 700 so as to be able to supply electric power to an electric motor 600. The hermetic terminal 702 is provided to pass through the hermetic container, and is positioned between an end coil of a stator 601 and the frame 400. In addition, a discharge pipe 701 is provided on an opposite side to the hermetic terminal 702 on the side surface of the hermetic container to pass through the hermetic container, and is provided above a balance weight 407.

The drive portion 3 for rotationally driving the orbiting scroll 200 is configured from base elements of the electric motor 600 having the stator 601 and a rotor 602, the rotational shaft 300, an oil supply pump 900, an Oldham coupling 500 constituting a rotation-preventing mechanism for the orbiting scroll, the frame 400, roller bearings 401, 803, the orbiting scroll bearing portion 203, the sliding bearing 210 disposed in the orbiting scroll bearing portion, and the like.

The rotational shaft 300 is configured from a main shaft portion 302, a crank pin 301 and an auxiliary bearing support portion 303. The main shaft portion 302 and the auxiliary bearing support portion 303 are formed coaxially to constitute a main shaft part, and further, the oil supply pump 900 is press-fitted into a lower end portion of the rotational shaft 300. The roller bearings 401, 803 rotatably support the main shaft portion 302 and the auxiliary bearing support portion 303, respectively, of the rotational shaft. The sliding bearing 210 is press-fitted in the orbiting scroll bearing portion 203, and is engaged with the crank pin 301 of the rotational shaft so as to be movable in an axial direction and rotatable.

The roller bearing 401 (the main bearing) is arranged on an upper side of the electric motor 600, and the roller bearing 803 (the auxiliary bearing) is arranged on a lower side of the electric motor 600. In the present embodiment, since the rotational shaft 300 is supported by the roller bearings 401, 803 in both sides of the electric motor 600, it is possible to suppress power loss and prevent the rotational shaft from tilting.

A housing 802 is fixed via a bolt 805 to a lower frame 801 fixed to the hermetic container 700, the roller bearing 803 is inserted in the housing 802 from above, and a housing cover 804 is further attached thereto from above.

The oil supply pump 900 is a centrifugal pump attached to the lower end of the rotational shaft 300, and forcibly supplies the lubricating oil stored in the oil reservoir 730 to the auxiliary bearing 803, the orbiting scroll bearing portion 203 and the main bearing 401 through an oil supply hole 901. The oil supplied to the oil supply hole 901 is also supplied to sliding portions of the orbiting scroll and the fixed scroll. The oil supply hole 901 is provided so as to pass through the rotational shaft 300 vertically, and has a lower oil supply hole which is concentric with respect to the axis of the rotational shaft and an upper oil supply hole which is eccentric with respect to the axis of the rotational axis. A lateral oil supply hole (the lateral hole) is provided so as to communicate with the lower oil supply hole to supply the oil to the auxiliary bearing 803.

The Oldham coupling 500 is disposed on the rear of the base plate 201 of the orbiting scroll 200. One of two set of orthogonal key portions formed in the Oldham coupling slides in a key groove formed in the frame 400, and the other set slides in a key groove formed in the rear side of the orbiting scroll spiral body 202. As a result, the orbiting scroll gyrates with respect to the fixed scroll 100 in a plane perpendicular to the axial direction in which direction the scroll spiral body is provided upright, without rotating on its own axis.

In the compression mechanism portion 2, when the crank pin 301 eccentrically rotates by rotation of the rotational shaft 300 coupled to the electric motor 600, the orbiting scroll gyrates with respect to the fixed scroll by the Oldham coupling (the rotation-preventing mechanism) to suck gas into the compression chamber 130 formed by the scroll spiral bodies 102 and 202 through the suction pipe 711 and the suction port 103. By the gyrating movement of the orbiting scroll, the compression chamber reduces the volume while moving to the central portion to compress the gas, and the compressed gas is discharged from the discharge port 104 to the discharge chamber. The gas discharged to the discharge chamber passes around the compression mechanism portion 2 to flow into an electric motor chamber, and is thereafter released from the discharge pipe 701 to the outside of the compressor.

A back pressure hole (not shown) providing communication between the compression chamber 130 and the back pressure chamber 411 on the rear side of the orbiting scroll is provided in the base plate 201 of the orbiting scroll 200, to maintain the pressure in a space of the back pressure chamber 411 outside a seal ring at a pressure (an intermediate pressure) between a suction pressure and a discharge pressure. The back pressure chamber 411 formed on the rear side of the orbiting scroll is a space formed by the orbiting scroll 200, the frame 400 and the fixed scroll 100. The frame 400 also serves as a member for forming the back pressure chamber 411, and the seal ring 410 provided in a groove of the frame 400 partitions the back pressure chamber 411 into an inner space substantially at the discharge pressure and an outer space at the intermediate pressure.

As shown in FIG. 2, the orbiting scroll 200 is pressed against the fixed scroll 100 through the seal ring 410 due to the resultant force by pressures in an inner space (the inner back pressure chamber) 412 which is substantially under a discharge pressure and an outer space (the outer back pressure chamber) 413 which is under an intermediate pressure. On the other hand, the orbiting scroll 200 receives force to be separated from the fixed scroll 100 by pressure in the compression chamber 130 formed by the orbiting scroll 200 and the fixed scroll 100. Accordingly, in order to press the orbiting scroll to the fixed scroll side with a proper force, the pressure (the intermediate pressure) in the space 413 outside the seal ring is set to satisfy the formula of:

Pressing Force≧Separating Force

As described above, in the present embodiment, while a pressure substantially corresponding to the discharge pressure acts in the inner space divided by the seal ring 410, and a pressure (an intermediate pressure) lower than that in the inner back pressure chamber acts in the space outside the seal member press the orbiting scroll against the fixed scroll, since the discharge pressure acts in the inner space 412, the force pressing the central portion of the orbiting scroll is far greater than the force pressing the outer peripheral portion side of the orbiting scroll. Accordingly, it has been found that there is the problem that surface pressures on the sliding surface of a tip end of the orbiting scroll spiral body 202 with respect to the fixed scroll 100 and the sliding surface of a tip end of the fixed scroll spiral body 102 with respect to the orbiting scroll 200 become excessive, which easily causes seizing and scoring.

In order to solve this problem, in the present embodiment, the shape of the spiral body 202 of the orbiting scroll 200 is configured such that the groove width of the spiral body decreases from the central portion toward the outside of the spiral body in a part of or the whole of the spiral body, and is formed such that the tooth thickness of the spiral body also decreases, as shown in FIGS. 3A and 3B. The spiral body 102 of the fixed scroll 100 is formed also in the same way as the spiral body 202 of the orbiting scroll.

It is more preferable to form the groove width and the tooth thickness of the spiral body formed inside the seal ring 410 to be larger than the groove width and the tooth thickness of the spiral body formed outside the seal ring. Such a spiral body shape can be fabricated by forming a part of or the whole of the spiral body by an involute of a circle (a base circle) a a radius of which varies in accordance with an involute angle. More specifically, the base circle for forming the spiral body formed inside the seal ring 410 is configured to have a radius larger than that of the base circle for forming the spiral body formed outside the seal ring 410.

Here, the spiral body of the scroll member can be formed by an involute of a circle represented by the formula of:

a=as+f(λ) (f′(λ)<0)

wherein a is the radius of the base circle, λ is the involute angle, and as is the radius of the base circle at the beginning portion of winding of the spiral body.

According to the present embodiment, by the above configuration, it is possible to increase the ratio of the area of the compression space under a higher pressure inside the seal ring with respect to the compression space outside the seal ring, so that depressing force on the orbiting scroll member can be increased, and as a result, it is possible to prevent pressing force of the orbiting scroll member from becoming excessively large. In particular, since the back pressure chamber (the inner space) inside the seal ring is substantially subjected to a discharge pressure, pressing force is strong in the central portion of the orbiting scroll. However, in the present embodiment, the area of the compression chamber under high pressure on the central portion side can be made larger among the compression chamber formed by both scroll members, and therefore separating force on the central portion side can be increased, and the surface pressures of the sliding surfaces of the tip ends of the spiral bodies of both scroll members can be maintained appropriately, which provide an effect of reliably preventing occurrence of seizing and scoring on the sliding surfaces.

In the meanwhile, if the spiral bodies of the scroll members have a shape in which the groove width and the tooth thickness are uniform over the whole spiral body from the central portion of the spiral body toward the outside like a conventional one, since the outermost diameter of the spiral body becomes large, the base plate 201 becomes large, the area which is subjected to the intermediate pressure becomes large, and the force to press the whole orbiting scroll against the fixed scroll becomes large. If the whole pressing force becomes large, the sliding resistance between the orbiting scroll base plate and the fixed scroll panel board surface also becomes large, which further increases the risk of scoring and seizing. It is conceivable to make the back pressure hole communicate with the lower pressure side of the compression chamber so as to set the intermediate pressure to be low, however, if the back pressure hole communicates with the lower pressure side of the compression chamber, since pressure fluctuation in that compression chamber is small, the pressure of the back pressure chamber under the intermediate pressure remains low even if the separating force generated by the pressure of the whole compression chamber fluctuates widely. Therefore, the value of the pressing force can not sufficiently follow the fluctuation of the separating force, which makes it impossible to expand the operating range.

In the present embodiment, since a part of or the whole of the spiral bodies is formed such that the groove width of the spiral bodies of both scroll members varies and the tooth thickness of the spiral bodies of both scroll members decreases from the center toward the outside of the spiral bodies, the outermost diameter of the spiral bodies can be made small and the scroll members can be reduced in diameter. In addition, since the area of the rear side of the orbiting scroll upon which the intermediate pressure acts can be made small, the pressure in the back pressure chamber upon which the intermediate pressure acts can be set larger. Therefore, according to the present embodiment, it becomes possible to make the back pressure hole communicate with the higher pressure side of the compression chamber and to allow the value of the pressing force to sufficiently follow the fluctuation of the separating force, so that the operation range can be readily expanded, and also an effect of further reducing the risk of scoring and seizing by reducing the sliding resistance between the orbiting scroll base plate and the fixed scroll panel board surface. As described above, according to the present embodiment, since the high pressure region in the back pressure chamber can be increased in comparison with the conventional scroll spiral bodies, the equilibrium of the forces in the axial direction of the orbiting scroll can be kept in a wider operation range.

Thus, according to the present embodiment, it is possible to obtain a scroll fluid machine which can improve the efficiency with high reliability and which can achieve reduction in diameter of scroll members.

In the present embodiment, the inner diameter of the seal ring 410 is smaller than the outer diameter of the roller bearing 401. Therefore, the embodiment is configured such that the roller bearing 401 is inserted from the electric motor side to the frame 400 and is fixed by a frame cover 403. The frame cover 403 is provided with a thrust bearing and is fixed to the frame 400 by a bolt 406. By this bolt fixation, the gap between the frame cover and the frame can be precisely sealed so that oil leakage from the oil supply path can be suppressed.

The balance weight 407 is pressed into the rotational shaft 300 in the electric motor side of the roller bearing 401 to be fixed there. The maximum outer diameter portion of the balance weight 407 is provided on an end surface side of the coil end of the stator 601 and has a diameter larger than the inner diameter of the coil end.

Next, the oil supply path will be described. When the rotational shaft 300 starts rotating, oil in the oil reservoir 730 under discharge pressure is supplied to an oil passage 311 in the rotational shaft by raising the pressure by the oil supply pump 900. A part of the oil fed to the oil passage 311 flows to the auxiliary bearing 803 through a lateral hole 312 and thereafter returns to the oil reservoir 730. The oil reaching an upper portion of the crank pin 301 through the oil passage 311 lubricates the sliding bearing (the gyration bearing) 210 and further flows to the roller bearing 401. Most of the oil having lubricated the roller bearing 401 returns to the oil reservoir 730 through an oil drain pipe 408. Since the space inside the seal ring 410 is supplied with the oil from the oil reservoir 730 which is under the discharge pressure, the space is filled with the oil substantially under the discharge pressure.

An oil supply pocket (a concave groove) 205 is formed in the end face of the orbiting scroll bearing portion 203. The oil supply pocket 205 reciprocates across the seal ring 410 between the outside and inside thereof by the gyrating movement of the orbiting scroll 200, and conveys a part of the oil existing between the sliding bearing 210 and the roller bearing 401 to the back pressure chamber 411 in the space outside the seal ring. The conveyed oil lubricates the Oldham coupling 500 as well as the sliding surfaces between a panel board surface 105 of the fixed scroll and the base plate 201 of the orbiting scroll 200. Thereafter, the oil flows into the compression chamber 130 through the back pressure hole or a minute gap of the panel board sliding surface. The oil flowing into the compression chamber 130 is discharged from the discharge port 104 together with the compressed refrigerant gas, is separated from the refrigerant gas in the hermetic container 700, and returns to the oil reservoir 730. The back pressure chamber 411 in the space outside the seal ring is substantially under the same pressure as the compression chamber communicating with the back pressure hole, that is, under the intermediate pressure between the discharge pressure and the suction pressure, due to the back pressure hole.

As mentioned above, the back pressure chamber of the orbiting scroll is constituted by the inner space under discharge pressure inside the seal ring and the outer space under intermediate pressure outside the seal ring, and the orbiting scroll receives pressing force according to the sum of the discharge pressure of the inner space and the intermediate pressure of the outer space. Since the orbiting scroll also receives separating force due to the pressure in the compression chamber formed by both scroll members, the orbiting scroll will be finally pressed to the fixed scroll side by the pressing force minus the separating force. Since the inner space is substantially under the discharge pressure, the pressing force at the central portion of the orbiting scroll becomes large. However, in the present embodiment, since the area of the compression chamber under high pressure on the central portion side among the compression chamber formed by both scroll members is configured to be larger, the separating force on the central portion side is also large. Consequently, the sliding surfaces of the tip ends of the spiral bodies of both scroll members can be maintained at a proper surface pressure.

The flow of oil and refrigerant gas discharged from the discharge port 104 will be described. The oil and the refrigerant gas discharged from the discharge port flow through the fixed scroll 100 and a passage (not shown) provided at the outer periphery of the frame 400 into a D partition 423 provided in a lower part of a leg portion 422 of the frame. The D partition 423 has two flow paths which are a window portion provided in the inner periphery direction of the hermetic container and a minute gap portion 424 provided at a lower end of the D partition. Most of the oil and the refrigerant gas flowing into the D partition 423 exit from the window portion provided in the inner periphery direction of the hermetic container, and flow in a space between the frame 400 and the stator 601 along the inner periphery of the hermetic container. A part of the oil and the refrigerant gas flowing out to the gap portion 424 provided at the lower end of the D partition 423 passes through a stator outer periphery passage (not shown) provided in the outer peripheral portion of the stator 601 and is utilized for cooling the stator 601.

In connection with the oil and refrigerant gas flowing along the inner periphery of the hermetic container 700, the oil with a greater specific gravity flows while attaching to the inner periphery of the hermetic container due to the effect of centrifugal force, and is separated from the refrigerant gas. The separated oil returns to the oil reservoir 730 through the stator outer periphery passage. The refrigerant gas is released out of the hermetic container through the discharge pipe 701.

It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims. 

1. A scroll fluid machine comprising two scroll members each of which has a spiral body formed on a base plate, the scroll members being engaged to relatively gyrate such that a hermetic space formed by both scroll members is increased or reduced to make fluid expand or compress the fluid, wherein: the scroll fluid machine is configured such that a seal member is provided between a rear surface of one of the scroll members and a stationary member to divide a space formed between the rear surface and the stationary member into an inner side space and an outer side space, the inner side space inside the seal member being subjected to a pressure substantially corresponding to a discharge pressure, the outer side space outside the seal member being subjected to a pressure lower than that in the inner side space to press the one scroll member against the other scroll member; and the shape of the spiral body of each scroll member is configured such that the width of a groove of the spiral body of the scroll member and the thickness of a tooth of the spiral body decrease from a central portion toward an outer side of the spiral body over a part of or the whole of the spiral body.
 2. The scroll fluid machine according to claim 1, wherein a part of or the whole of the spiral body of each scroll member is formed by an involute of a circle (base circle) the radius of which varies depending on an involute angle.
 3. The scroll fluid machine according to claim 1, wherein each scroll member is formed such that the width of a groove and the thickness of a tooth of the spiral body formed inside the seal member are larger than those of the spiral body formed outside the seal member.
 4. The scroll fluid machine according to claim 2, wherein each scroll member is formed such that a radius of the base circle for forming the spiral body formed inside the seal member is larger than that of the base circle for forming the spiral body formed outside the seal member.
 5. The scroll fluid machine according to claim 4, wherein the spiral body of each scroll member is formed by an involute of a circle represented by the formula of: a=as+f(λ) (f′(λ)<0) wherein a is a radius of the base circle, λ is an involute angle, and as is a radius of the base circle at a beginning portion of winding of the spiral body.
 6. A scroll fluid machine comprising a fixed scroll and an orbiting scroll each of which has a spiral body formed on a base plate, the fixed scroll and the orbiting scroll being engaged, wherein: the scroll fluid machine is configured such that a seal member is provided between a rear surface of the orbiting scroll and a frame member arranged opposite to the rear surface to divide a space formed between the rear surface and the frame member into an inner side space and an outer side space, the inner side space inside the seal member being subjected to a pressure substantially corresponding to a discharge pressure, the outer side space outside the seal member being subjected to a pressure lower than that in the inner side space to press the orbiting scroll against the fixed scroll; and each of the orbiting scroll and the fixed scroll is formed such that the width of a groove and the thickness of a tooth of the spiral body formed inside the seal member are larger than those of the spiral body formed outside the seal member. 